To this point, over 90 patients (most with melanoma and including a dozen with objective clinical responses) have had serum and peripheral blood mononuclear cells (PBMC) collected during their initial therapy with IL-2. Over 30 immune related proteins have been interrogated in pretreatment sera by multiplex assay. The pre-treatment PBMC and the PBMC rebound occuring after stopping IL2 have been subjected to Affymetics array analysis in a test set and we are accumulating a validation set of samples. We have also entered into a collaboration with MD Anderson CC to exchange anonymous samples from patients treated with high dose IL2 to use as part of the validation set.Finding molecular factors associated with one of the only curative therapies for melanoma and renal cancer would not only allow treatment to focus on those most likely to benefit, but it could also provide clues to the mechanism by which IL-2 is working.